The invention relates to a volume-controlled four-stroke reciprocating internal combustion engine as well as a method for operating the four-stroke reciprocating internal combustion engine.
For the technical background, reference is made, for example, to the translation of German patent DE 696 00 937 T2, from which an adjustment of the camshaft phase for deactivation of a cylinder of a reciprocating internal combustion engine is known. This patent discloses a multi-cylinder four-stroke reciprocating internal combustion engine with a crankshaft and a plurality of pistons reciprocating in a plurality of cylinders. Furthermore, each cylinder of the internal combustion engine has at least one intake valve and one exhaust valve as well as a camshaft for actuating at least the exhaust valves. This internal combustion engine is characterized in that it also has the following features:                a phase control mechanism for adjustment of the camshaft timing with regard to the rotational position of the crankshaft;        a plurality of intake throttles, wherein one of the throttles is disposed near to and upstream of each of the intake valves; and        a controller connected to the intake throttles and to the phase control mechanism for the camshaft for deactivation of at least some of the cylinders by actuation of the phase control mechanism and the inlet throttles in such a way that for each cylinder to be deactivated the intake throttle is closed and the camshaft controller is adjusted in such a way that the position with maximum exhaust valve lift is moved from approximately 90° before the top dead center in the exhaust stroke to a point at which the maximum valve lift occurs either approximately at top dead center of the exhaust stroke or approximately at bottom dead center of the expansion stroke.        
The starting point for the invention is the German patent application No. DE 10 2011 006 388.9 from which a method for operating a volume-controlled internal combustion engine and an internal combustion engine provided therein are known. The internal combustion engine has at least two cylinders, as well as an intake duct and an exhaust gas system. An expansion/compression machine of which the output shaft can be coupled to an output shaft of the internal combustion engine and/or to a drive shaft of an electric machine is disposed in the intake tract in the direction of flow of the fresh air before an intake valve of the internal combustion engine. Furthermore, a heat exchanger is disposed on the exhaust gas system. The method is characterized in that before the fresh air flows into the expansion/compression machine it is heated in the heat exchanger by the exhaust gas from the internal combustion engine. The efficiency of the internal combustion engine is substantially improved by the method for operating the volume-controlled internal combustion engine.
In the above-mentioned patent application, it is stated that by the use of the expansion process not only are the charge exchange losses avoided but, in connection with the exhaust gas heat exchanger according to the invention, clear efficiency advantages and thus fuel consumption advantages are achieved. Furthermore, this technology can be combined particularly well with exhaust gas turbocharging. Therefore, in this patent application the efficient load control (ELC) of a volume-controlled internal combustion engine is also mentioned.
Similar to the way in which the power of the internal combustion engine can be increased by a mechanically or electrically driven compressor in the intake tract by compression of the fresh air, by means of an expansion machine, which can simultaneously be designed as a compression machine instead of the throttle valve, the fresh air can be “diluted”, i.e. can be adjusted to a lower density and thus the power of the internal combustion engine can be reduced. As a result, throttle losses of a conventional throttle valve are practically entirely avoided. The efficiency advantage is comparable to a variable valve control, as has already been used for example by Bayerische Motoren Werke AG for over a decade in mass production under the name “Valvetronic.” The work which is performed in the expansion machine can be delivered by way of a mechanical coupling (for example a belt drive) to the internal combustion engine or to the crankshaft thereof or to an electric generator.
As is also stated in the above-mentioned patent application, further increases in efficiency in the partial load of the internal combustion engine can be achieved if thermal energy is transferred to the fresh air by way of the heat exchanger on the exhaust gas system. As a result, the volume flow of the fresh air is thereby increased and also, proportionally thereto, the work which is performed in the expansion/compression machine. After the expansion/compression machine, the fresh air is cooled by a cooler, e.g. a charge air cooler, again to the usual fresh air temperature, before it is fed to the internal combustion engine for combustion. Thus, efficiencies which are clearly above those of a stroke- and/or time-variable valve drive can be achieved in the partial load range of a volume-controlled internal combustion engine. This corresponds to the known prior art.
A disadvantage of this prior art is the use of a separate expansion/compression machine which requires installation space and incurs production costs as well as an expensive coupling to the power supply.
The object of the present invention is to provide a generic volume-controlled four-stroke reciprocating internal combustion engine which does not have a separate expansion/compression machine, and also suitable methods for operating this four-stroke reciprocating internal combustion engine.